watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-30T17:21:52Z. The update package is 77.01 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 23999eb9a65f5605634b49f86a8563f93dd3ef95.zip.